A geophysical survey is the systematic collection of geophysical data for spatial studies. Detection and analysis of geophysical signals form the core of geophysical signal processing. The geophysical survey uses various sensing instruments, and data may be collected above or below the Earth’s surface, on airborne, orbital, or marine platforms. Geophysical surveys have applications in many disciplines, including geology, archaeology, environmental science, and engineering. They are also used in industrial and academic research.
Techniques and Equipment Used in Geophysical Surveys:
Gravity: Measures variations in Earth’s gravitational field.
Seismic: Seismic surveys use sound waves to map underground structures.
Radioactive: Detects radioactive elements underground.
Magnetics: This survey measures the Earth’s magnetic field variations caused by underlying rocks.
Electromagnetics: Electromagnetics surveys use electromagnetic fields to detect conductive materials beneath the surface.
Resistivity: This survey measures electrical resistance in the ground, identifying areas with different soil types, water content, and mineral concentrations.
Radar: Uses radio waves for subsurface mapping.
Active and Passive Geophysical Surveys:
Active: Artificial Controlled Signal Source
Passive: Natural Source
Method
Active Survey
Passive Survey
Seismic
Refraction Reflection Surface wave
Microtremor
Gravitation
Gravity
Magnetic
Magnetic
Electric
VES, 2-D, IP
SP
Electromagnetic
CSAMT, TEM, GPR
AMT
Geophysical Surveying Applications:
Application
Area Appropriate Methods
Exploration for fossil fuels (Oil, Gas & Coal)
S, G, M, (EM)
Exploration for metalliferous minerals
M, EM, E, SP, IP
Exploration for bulk mineral deposits ( Sand & gravels)
S, (E), (G)
Exploration for groundwater,
E, S, (G)
Engineering and Construction investigations
E, S, (G), (M)
Limitation of Geophysical Surveys:
Assumption on analysis
For example, VES (Vertical Electric Sounding)
Horizontal layered structure
No variation of underground structure for the horizontal direction
Trading off between Resolution and Exploration depth
The deeper, the less resolution
Trading off between Resolution and Noise
The more extensive the resolution, the more significant the error
